JPH0541649A - Electronic timer circuit - Google Patents

Abstract

PURPOSE:To reduce the change of a timer value after the temperature change and long-term use. CONSTITUTION:A thermosensitive resistor R5 with the positive temperature characteristic is parallely connected to the capacitor of a serial CR time constant circuit composed of a resistor R1 and a capacitor C1. Thus, even when the capacity of the capacitor C1 deteriorates at the time of low temperature, the influence of the thermosensitive resistor R5 can be reduced. If the electronic timer circuit is used after the long period of nonuse, the change to the time constant due to the increase of the leakage current can be reduced since the resistor R5 is parallely connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic timer circuit using a time constant circuit composed of a resistor and a capacitor.

[0002]

2. Description of the Related Art An example of a conventional off-delay type electronic timer circuit for delaying a signal by using a resistor and an aluminum electrolytic type capacitor as a time constant circuit is shown in FIG. In the figure, the output terminal from the output transistor 1a provided in the switch circuit is connected to the common connection terminal of the resistor R1 and the electrolytic capacitor C1 via the diode D1. Resistance R1,
The capacitor C1 is a time constant circuit connected between the power supply terminals 2 and 3 as shown, and a series connection body of resistors R2 and R3 is also connected between the power supply terminals. Resistors R2, R3
The middle point is connected as a reference voltage Vref to the reference input terminal of the comparator 4, and the other input terminal has a resistor R1 and a capacitor C1.
The common connection ends of are connected.

In such an off-delay type electronic timer circuit, the internal transistor 1a is on when the switch circuit 1 is not detecting an object, the terminal voltage of the capacitor C1 is low, and the diode D1 and the transistor 1a are connected. Is discharging through. When an object is detected, the transistor 1a is turned off, so that the resistance R1
The capacitor C1 is charged via. A curve A in FIG. 6 shows a temporal change in the terminal voltage of the capacitor at this time, and this terminal voltage is a threshold value V determined by the resistors R2 and R3.
When it exceeds ref, the output of the comparator 4 is inverted and the switch signal is output from the comparator 4 to the outside. This timer time is T1.

[0004]

However, in such a conventional electronic timer circuit, the capacity of the aluminum electrolytic capacitor greatly changes depending on the temperature. FIG. 7 is a graph showing the temperature characteristics of the aluminum electrolytic capacitor. Since the capacity of the aluminum electrolytic capacitor decreases significantly as the ambient temperature decreases, the change in the terminal voltage of the capacitor C1 is shown by the broken line B in FIG. 6 especially at low temperatures. Changes to. Therefore, there is a drawback that the off-delay timer time is shortened from T1 to T2.

When the electronic timer circuit is left unused for a long period of time and then used, the switch output of the switch circuit greatly increases the current flowing through the capacitor C1. This is equivalent to a reduction in the resistance value of the resistor R4 which is considered to be equivalently inserted in the capacitor C1. Normally, the resistance value of the resistor R4 equivalently connected to the capacitor C1 is sufficiently large, for example, 100 MΩ,
The terminal voltage of the capacitor rises to Vcc. However, if the electronic timer circuit is not used for a long period of time, the saturation voltage at the time of charging will change as shown by the broken line C in FIG. 8 because the leakage current becomes large. For example, when the resistance R1 is 500 to 1 MΩ and the resistance R4 is 2 to 3 MΩ, the peak value is reduced by about 40%. In this case, the operating time of the electronic timer circuit is the specified value T
There is a drawback that the time T3 (T1 <T3) is significantly longer than 1.

The present invention has been made in view of such problems of the conventional electronic timer circuit, and it is a technical object to make it possible to stabilize the operation time of the electronic timer circuit with a simple structure. To do.

[0007]

The present invention is an electronic timer circuit having a CR circuit including a capacitor and a resistor connected to the capacitor, and a comparison circuit for comparing a terminal voltage of the capacitor of the CR circuit with a reference voltage. Then, a temperature-sensitive resistor having a positive temperature characteristic is connected in parallel with the capacitor.

[0008]

According to the present invention having such characteristics, since the temperature-sensitive resistor having the positive temperature characteristic is connected in parallel to the capacitor, the charging characteristic has a long rise time of the terminal voltage of the capacitor when the resistance. , Which cancels out the change in the capacitance of the capacitor and reduces the amount of change in the timer time. When the capacitor is not used for a long period of time, the leakage current of the capacitor becomes large and the equivalent resistance value connected in parallel corresponding to this becomes small. The amounts are offset, and the amount of change in operating time can be reduced.

[0009]

1 is a circuit diagram showing the structure of an electronic timer circuit according to an embodiment of the present invention. The same parts as those of the conventional example described above are designated by the same reference numerals and detailed description thereof will be omitted. Also in this embodiment, the switch circuit 1 is connected between the power supply terminals 2 and 3, and the collector end of the transistor 1a inside the switch circuit 1 has the resistor R1 and the capacitor C via the diode D1.
1 connected to a time constant circuit. The voltage at the midpoint of the time constant circuit is given to the comparison input terminal of the comparator 4, and the other input terminal of the comparator 4 is connected to the reference voltage source composed of the resistors R2 and R3. In this embodiment, a temperature sensitive resistor R5 is connected in parallel with the electrolytic capacitor C1 as shown in the figure.
The temperature-sensitive resistor R5 has a positive temperature characteristic and has a characteristic that the resistance value decreases as the temperature decreases. For this temperature coefficient, for example, the rate of change in resistance per 10 ° C is 0.15 to 5%,
It is assumed that the resistance value changes linearly as shown in FIG. 2 according to the temperature change. Other configurations are the same as those of the conventional example described above.

Next, the operation of this embodiment will be described. In such an electronic timer circuit, if the switch circuit 1 does not detect an object, the internal transistor 1a is on and the capacitor C1 is discharged. When the switch circuit 1 detects an object, the transistor 1a is turned off and the capacitor C1 is charged via the resistor R1. Here, the resistance value of the temperature-sensitive resistor R5 at room temperature is R5a
Then, the voltage change of the capacitor C1 applied to the inverting input terminal of the comparator 4 changes as shown by the curve D in FIG.
This peak value is expressed by the following equation (1). Vcc · R5a / (R5a + R1) (1) And the resistance value of the temperature sensitive resistor R5 is small at low temperature R5b
Therefore, the saturation characteristic changes and the peak value decreases as shown by the following equation (2). Vcc · R5b / (R5b + R1) (2) If the capacitance of the capacitor C1 does not change, the saturation characteristic changes as indicated by the broken line E in FIG. 3, and the off-delay timer value T4 becomes Longer direction (T4> T
Change to 1). Actually, since the capacity of the capacitor C1 decreases at low temperature, the timer value changes so as to become shorter as shown in the conventional example. By offsetting such changes, it is possible to obtain a delay time close to the off-delay time at room temperature even at low temperatures.

When the electronic timer is used again after it has not been used for a long time, the current flowing through the capacitor C1 increases. This is recognized as a state where the resistance value of the equivalent resistance R6 corresponding to the leakage current which is considered to be connected in parallel with the capacitor C1 decreases. When the equivalent resistance R6 is included, the maximum voltage during charging of the capacitor is shown by the following equation (3) as shown in FIG.

[Equation 1] Here, R6 is negligible because it is, for example, several hundred MΩ during normal use, and the change in the terminal voltage of the capacitor C1 becomes the curve D in FIG. The terminal voltage in this case is represented by Expression (1).

The maximum value of the terminal voltage when the electronic timer is used after being used for a long time is similarly expressed by the equation (3), but the resistor R6 cannot be ignored. For example, the resistance value R6 of the equivalent resistance corresponding to the leakage current is set to 2 to 3M.
Assuming that Ω and R5 are 250K to 1MΩ, the resistor R1 is 500K to 1MΩ, and the capacitor C is 47μF, the peak voltage of about 20% decreases as shown by the broken line F in FIG. However, in this embodiment, since the temperature-sensitive resistor R5 is connected in parallel, the change amount of the timer time can be made relatively small from T1 to T5. Then, it will be restored to the original state after several uses.

[0013]

As described above in detail, according to the present invention, since the temperature sensitive resistor having the positive temperature characteristic is connected in parallel to the capacitor of the CR time constant circuit, the operation time is kept low even at a low temperature. Changes can be reduced. If the capacitor is not used for a long period of time, the leakage current of the capacitor will increase, but in this case as well, the resistors are connected in parallel, so the amount of change can be reduced and the change in the operating time of the electronic timer circuit can be reduced. The effect of being able to do is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an electronic timer circuit according to an embodiment of the present invention.

FIG. 2 is a graph showing changes in resistance of the temperature-sensitive element having a positive characteristic used in this embodiment.

FIG. 3 is a graph showing changes in the terminal voltage of the capacitor when the electronic timer circuit of this embodiment is used at room temperature and low temperature.

FIG. 4 is a graph showing changes in the terminal voltage of the capacitor when the electronic timer circuit is used after a long period of non-use.

FIG. 5 is a circuit diagram showing a configuration of a conventional electronic timer circuit.

FIG. 6 is a graph showing a change in capacitance of an aluminum electrolytic capacitor with respect to ambient temperature.

FIG. 7 is a graph showing changes in the terminal voltage of the capacitor of the conventional electronic timer circuit at room temperature and at low temperature.

FIG. 8 is a graph showing changes in the terminal voltage of the capacitor when the conventional electronic timer circuit is used for a long period of time after being unused.

[Explanation of symbols]

 1 switch circuit 2, 3 power supply 4 comparator R1 to R3 resistance R4, R6 equivalent resistance R5 temperature sensitive resistance C1 capacitor

Claims (1)

[Claims] 1. An electronic timer circuit comprising: a CR circuit including a capacitor and a resistor connected to the capacitor; and a comparison circuit for comparing a terminal voltage of the capacitor of the CR circuit with a reference voltage. An electronic timer circuit characterized by connecting a temperature-sensitive resistor having a positive temperature characteristic.